Variable pitch propeller



Sept. 12, 1939. E B, c RNs 2,172,932

VARIABLE PI TCH PROPELLER Filed April 26, 1937 g INVENTOR 4; ATTORNEY- Patented Sept. 12, 1939 UNITED STATES PATENT. OFFICE Application April 26, 1937, S erial No. 138,900

1 Claim.

This invention relates to variable pitch aeroplane propellers and particularly to the typ that may be manually controlled from the cockpit of an aeroplane.

Controllable pitch propellers, both manually and automatically operable, are well known in the aeroplane industry and are commonly used on many types of aeroplanes. The types nowin use, however, are'relatively complicated in construction and are therefore expensive to manufacture. Also, such propellers while capable of Variation in pitch, are not generally adapted to be varied in length. As a consequence, the greatest possible. efliciency has not been obtained from them in actual use.

It has been found desirable to extend the blades of the propeller when they are at a lowerpitch.

During climbing when great lifting power is required, propellers are normally operated at low pitch and high rotational speeds. By lengthen! ing the propeller more air traction results, or when the propeller is useil as a pusher, more thrust is delivered.

When cruising, however, it has been found that a shorter propeller of greater pitch is the most eflicient. Due to the characteristics of propellers their effectiveness is gaged by their slippage loss. If the pitch of the propeller plane flies at a cruising angle of low drag, the propeller will race at a speed deteriorating to the motor driving the propeller.

An object of the invention is to produce a propeller in which the blades are controllable as to pitch and the.propeller is variable as to over all length, the pitch and length varying simultaneously.

A furtherobject of the invention is to provide an easily manufactured construction in which the blades are rotatably mounted in a hub through a construction which also acts to extend or retract the blades in the hub on rotation.

A still further object of the invention is to provide manually controllable means for varying the relationship of the blades to the propeller hub, the

principal parts of which'are attached to and supported on the aeroplane engine.

My improved propeller a hub member fixed on the propeller shaft and having any desired number of laterally extending sleeves, for example two or more, in which the blades are rotatably mounted. The sleeves are preferably provided with internal threads into which cylindrical ends on the blades are threaded 'to form a firm connection, allowing both rotation of the blades to control their pitch, and to extend is too Jew and the may suitably consist of or retract them. The sleeves may be arranged radially of the hub or offset therefrom as desired. The blades may be rotated to vary their pitch by-racks movable axially of the propeller shaft in engagement with gears carried by the blades. .5 The racksmay be shifted axially ofthe propeller shaft through a couplingmounted on the adjacent end of the crankcase or housing of the aeroplane engine, the coupling being operatively connected to manually operated controls mounted in 10 the cockpit of the aeroplane. For a better understanding of the present invention, reference may be had to the accompanying drawing, in which: a

Figure 1 is a view in section of a typical form oi 15 propeller embodying the invention; and v v Figure 2 is a view in section, taken on line 2-2 .of Figure 1.

In the form of the invention illustrated in Figure 1 the propeller hub l0 may be fixed to the 0 propeller shaft i2 in any suitable manner, such as by the .spline B, to cause the hub construction to rotate with the propeller shaft. The hub III may be formed of any suitable type of lightweight metal and may be provided with laterallypro- 5 iecting sleeves I4 and I6 forming sockets for receiving propeller blades. The sleeves l4 and ii are provided with internal threads l8, which engage complementarily threaded cylindrical ends 20 on the propeller blades 22 and 24. The 30 threaded connection between the blades 22 and 24 and sleeves i4 and I6, respectively, attaches the blades to the hub Hi so that they will not be thrown out of the hub by the centrifugal force generated during rotation of the propeller.

However, the threaded connections allow the blades 22 and 24 to be rotated on their longitudinal axes varying their pitch and at'the same time moving them inwardly or outwardly from the sleeves H and It as an incident to their rotation. The threads on the propeller blades and in the sleeves I4 and I6; are so related that a decrease in pitch of the blades results in longitudinal outward movement of the blades, and increase. in pitch decreases the length of the propeller.

The blades are preferably adapted to be rotated by means of identical rack elements 28 and 28 ailixed to a ring '30 and being spaced diametrically of the ring with their toothed faces lying in spaced parallel planes. The racks 26 and 28 extend through holes in the hub l0 into mesh with gears 30 and 32, respectively, fixed on the ends of theblades 22 and so that movement of the racks axially of the propeller shaft l2 will cause the blades to rotate on their longitudinal axes.

' The gears 30 and 32 are preferably wider than the racks 26 and 28 so that the inward and outward movement of the propeller blades 22 and 24 in the sleeves l4 and I6 will not move the gears out of engagement with the racks.

The racks 26 and 28 may be inserted into the hub i0 and retained in engagement with the gears 38 and 32 by means of shims 34 and 36 which are placed in back of the racks after their insertion into the propeller hub. The shims may either be fixed to the racks or fixed in the hub, as desired.

The racks 28 and 28 are adapted to be moved axially of the propeller shaft by means of a sleeve 38 threaded on the bearing housing 40 of the aeroplane motor. When the sleeve 38 is rotated it is moved axially of the propeller shaft I! also moving the racks 28 and 28. As best shown in Figure 1, the axial movement of the sleeve -38 is transmitted through a ball thrust bearing 42 mounted between a flange 44 on the sleeve 38 and a flange 48 on the ring 30 supporting the rack members. The flange 44 may be attached to the sleeve 88 through a threaded connection, allowing ready connection of the sleeve 88 to the ring 30. Likewise, the ring 30 may be provided with an outwardly projecting flange 48 to which is attached by set screws an inwardly extending annular, flange bearing against one side of the ball bearings 42 and forming one side of the ball race. This construction also aids in connecting the sleeve 38 to the ring 38.

The sleeve 88 may be rotated on the journal 40 of the engine by means of a pinion 82 rotatably mounted on a stub shaft 54 threaded in a socket 56 on the engine, the pinion 52 meshing with elongated gear teeth 88 on the sleeve 38. The pinion 52 may be driven by a gear 88 on a shaft 82 extending fromrthe front of the aeroplane into the cockpit where it may be provided with a crank or hand wheel, not shown. Ii desired stop means may be provided for limiting the displacement of the sleeve 38, ring 88, or the racks to determine the maximum variation in pitch of the propeller.

Vifith this construction it is possible for the operator of the aeroplane to control the pitch and length of the propeller so as to give it its highest possible efliciency. The construction above described is simple, has but comparatively few parts, and may be manufactured at little expense, and yet, at the same time, will provide a highly eflicient and practical construction for varying the pitch of the propeller.

It will be understood that the above described embodiment is illustrative only as it is susceptible to much variation without departing from the invention, and therefore should not be considered as limiting the scope of the following claim.

Iclaim:

In a variable pitch propeller, tne combination of an engine shaft, an externally threaded journal for the shaft on said engine, a hub fixed to the shaft, internally threaded sockets in said hub, propeller blades, externally threaded inner ends on said blades screwed in said sockets, a ring disposed externally of said hub, parallel racks on said ring projecting into said hub, gears fixed on the propeller blades meshingwith the racks, an internally threaded gear on said ioumal, an outwardly opening annular channel member on the threaded gear, a flange on the ring projecting inwardly into the chamber member, antifriction means interposed between the channel member and the flange to connect the racks to the threaded gear I for simultaneous movement-axially of the shaft and for relative rotary movement, and a manually actuated gear for rotating the threaded gear to move the racks axially of the shaft and rotate the propeller blades about their axes.

EDMUND '.B.- CAIRNS. 

